Vector Algebra Question 355
Question: The position vector of vertices of a triangle ABC are $ 4\mathbf{i}-2\mathbf{j},,\mathbf{i}+4\mathbf{j}-3\mathbf{k} $ and $ -\mathbf{i}+5\mathbf{j}+\mathbf{k} $ respectively, then $ \angle ABC= $
[RPET 1988, 97]
Options:
A) $ \pi /6 $
B) $ \pi /4 $
C) $ \pi /3 $
D) $ \pi /2 $
Show Answer
Answer:
Correct Answer: D
Solution:
- Here $ \overrightarrow{AB}=-3\mathbf{i}+6\mathbf{j}-3\mathbf{k}, $ $ \overrightarrow{BC}=-2\mathbf{i}+\mathbf{j}+4\mathbf{k} $ and $ \overrightarrow{AB},.,\overrightarrow{BC}=6+6-12=0\Rightarrow \angle ABC=90{}^\circ . $
BETA
